In this work, in order to model and analyse a simplified trophic network of the Venice Lagoon, I worked with the process algebra Bio-PEPA. This work shows that Bio-PEPA naturally permits the modelling of trophic networks and the analysis of their continuous dynamics. Different simulation and analysis techniques can be combined: discrete stochastic and continuous deterministic models can be automatically generated from a Bio-PEPA model. Specifically, it is possible to observe the dynamics of the populations of the species in a trophic network, understand the relationship among these species and predict the consequences of the perturbations of the ecosystem.